Tuning by ears is an important skill for musicians, learning that is beneficial. For example, you cannot rely on apps to tune your signing voice during performance.
The best army/weapon are those never needed to be utilized. Enemies won't pick up fights because your weapon/army are way stronger than theirs. Therefore we cannot regard army/weapon as "not used" or just wasted.
1. Pure gold will react with mercury and halogens. Yes, pure gold does "rot", just at lower rate, but still happens.
2. Most of the physical gold products, even at 99.99% pure, has 0.001% other elements which do rot too.
F-4 Phantom was a great fighter serving US Navy, Marine and Air Force. It equipped with missiles to kill enemies in the beyond visual range, didn't equip internal guns in the first generation because "it shouldn't get into close combat" .....